Alfven waves are ubiquitous in space and laboratory plasma. As Hannes Alfven himself described them as electromagnetic-hydromagnetic waves in 1942, magnetohydrodynamic (MHD) approach is often useful in understanding Alfven waves. However, it is also found that energetic particles rather than hydrodynamic motion are responsible for generation of certain types of Alfven waves called poloidal modes in the magnetosphere through wave-particle interaction and/or kinetic instabilities. One of most important and long-standing questions in Alfven waves can be how these poloidal Alfven waves are often observed for a long time even at the absence of corresponding driving sources, but no theories have been available yet. Recently, we have developed a theory on the existence of long-lasting poloidal Alfven waves, which will successfully illustrate how the energetic particles excite Alfven waves and then keep them persist in space. We also present a statistical database to compare its events with our theoretical conditions, which are very consistent with the observations.